Why is it 'Black' Friday?

Black Friday got its name because it has historically been the day when a surge of shoppers helped stores break into profitability or "into the black" for the full year.

It's not the biggest shopping day of the year, as that title belongs to days closer to the Christmas holiday. It's also not a predictor of holiday sales, but it remains an important barometer of people's willingness to spend for the rest of the season.

To that end, the National Retail Federation said earlier this month that it expects up to 138 million people to be shopping through Sunday, up from 134 million people a year ago.